Field
The present disclosure relates to semiconductor manufacturing and processing. More particularly, the disclosure relates to a process and apparatus for detecting substrate misalignment (i.e., position displacement error) and/or substrate support (e.g., susceptor) misalignment.
Description of the Related Art
In a semiconductor device fabrication process, such as CVD, epitaxy, or other thermal processing, substrates are often processed within chambers or other processing apparatuses. In order to process a substrate within the chamber, the substrate may be firmly attached to a substrate support within the chamber during processing to mitigate movement of the substrate. If the substrate support degrades over time, the substrate may no longer be firmly adhered to the substrate support, causing the substrate to move (which may cause substrate misalignment). Additionally, the substrate support may not rotate evenly and become misaligned. Numerous other factors may also lead to the substrate becoming misaligned. If the substrate becomes misaligned, uniformity in thickness and/or film properties may be adversely impacted.
Some semiconductor device fabrication processing systems may transfer a substrate between multiple chambers each having substrate support structures, for example, a deposition apparatus, an etching apparatus, an inspection apparatus, and the like. Such substrate exchange handling can result in significant slippage due to improper alignment. The substrate can be transferred between chambers by a transfer arm having a fork or an end effector. When the substrate support structures within a processing system are improperly aligned, the support structures do not hold the substrates at about the same inclination, or tilt. Thus, when one support structure transfers a substrate to another support structure, such as when the lift pins remove a substrate from a blade of the transfer chamber substrate handler or place a substrate onto the substrate support in a process chamber, one point of the substrate will always touch the receiving support structure before other points do. If substantial motion occurs prior to the remaining points making contact, then the substrate can slip. In this manner, potentially contaminating particles may be scraped from the contacting points of the substrate causing backside contamination of the substrate. These particles may eventually work their way around to the top of the substrate and be deposited on the processed surface of the substrate, thereby contaminating the micro circuits or other structures constructed thereon. Additionally, when the substrate does not touch a receiving support structure with all points in very close alignment, then the substrate may be shifted from its proper, or expected, position, so that the substrate is off-center. As mentioned above, an off-center substrate may undergo uneven or otherwise improper processing or may come in contact with surfaces or objects within the processing system that will contaminate the substrate, create potentially contaminating airborne particles or even break the substrate.
The need for placement accuracy is illustrated in prior art FIG. 1. A typical substrate 10 and a substrate support, e.g., a susceptor 12 for holding the substrate 10 within a single-substrate processing chamber, are depicted therein. For a given substrate 10, the pocket on a susceptor 12 which receives the substrate 10 generally has a diameter only slightly larger than that of the substrate 10. There is often a very small clearance 14 between the edge of the substrate 10 and the edge of the susceptor 12 pocket. The substrate 10 is centered in the pocket and a gap is maintained between the edge of the substrate 10 and the sidewalls of the pocket. If the substrate 10 has contact with the sidewalls of the pocket, local temperature changes occur, resulting in temperature gradients across the substrate 10. This can cause non-uniformity in process results, as most semiconductor processing depends critically on temperature. Similarly, uncentered substrates can be damaged during placement in a number of different handling situations.
During semiconductor processing, particularly during thermal processing, a substrate being supported by a traditional substrate support may warp, bow, and even break due to the thermal gradient caused by rapid thermal heating. In some cases, the deformation of the substrate may lead to thermal non-uniformity across the substrate because deformation causes different areas of the substrate to have different exposure to the heat sources. In high temperature deposition processes, different materials may shrink at different rates due to having different properties. This may cause a stack to stress and bow, producing a warped shaped. Also, the substrate may bow or warp due to thermal forces in the chamber. Moreover, layers may undergo stress changes when exposed to high temperatures, which can also lead to warping. Substrate bow and warping may have undesirable effects, such as limiting the number of layers that can be stacked.
One approach for determining position of a substrate, edge ring, and/or susceptor involves imaging. A device capable of imaging, such as a camera, can be used to detect position. Conventional imaging techniques for determining substrate, edge ring, and/or susceptor position use edge detection. Edge detection is a technique for identifying points in a digital image at which the image brightness changes sharply or, more formally, has discontinuities. The points at which image brightness changes sharply are typically organized into a set of curved line segments referred to as “edges”. Edge detection is a fundamental tool in image processing, machine vision and computer vision, particularly in the areas of feature detection and feature extraction. However, low image brightness or contrast can lead to unacceptable error in edge detection using conventional techniques.
Therefore, a need exists for an apparatus and method for determining the position of substrates and/or various substrate handling mechanisms of a processing system.